TRIUMF Neutral Atom Trap for beta decay angular correlations: searches for new interactions

用于 β 衰变角相关性的 TRIUMF 中性原子陷阱：寻找新的相互作用

• 批准号: SAPPJ-2019-00037
• 负责人: Behr, John
• 金额: $ 10.53万
• 依托单位: TRIUMF
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=764734
• 关键词: TRIUMF; Neutral; Atom; Trap; beta

Nuclear beta decay correlation experiments helped establish the nature of the weak interaction, a theory with spin-1 bosons (like the photon, but massive) coupling only to left-handed leptons (i.e. electrons and neutrinos). The angular distribution of the outgoing particles, if measured to part per thousand, is sensitive to new interactions that can produce leptons with different handedness. We have measured the beta asymmetry with respect to the nuclear spin in 37K decay to be Abeta=-0.5706+-0.0018. This was C.S. Wu's original parity-violating observable, and our beta asymmetry measurement has the best fractional accuracy (i.e. smallest uncertainty/Abeta) in any nucleus or the neutron, and is in agreement with theory. Our average value of Abeta can either constrain interactions producing wrong-handed neutrinos, or, combined with other experiments, tests whether nuclei with finite spin and magnetic moment all have the same intrinsic strength of beta decay. We will further explore this possible "conserved vector current" violation by measuring Abeta and other observables better in 37K. The dependence of Abeta on beta energy is still under analysis by a Ph.D. student, and is separately sensitive to new 4-fermion effective field theory interactions. Our proposed measurements, including the asymmetry of the direction of progeny nuclei with respect to the intial nuclear spin, probe new interactions producing wrong-handed positrons: these observables scale with a helicity factor (electron mass)/(electron energy) that is typically suppressed at higher energy, making our measurements complementary. Key to our measurements is our demonstrated ability to highly polarize the nuclei with our atom trap techniques, and to determine the polarization of the nuclei decaying to 0.1% accuracy by atomic methods in situ. We also plan a time reversal symmetry test using the three independent momenta of the products of radiative beta decay, a unique test in the first generation of particles at relatively low energy scale. Reactor neutrinos show anomalies in their total number and energy dependence. We are reconstructing the neutrino energy spectrum from 92Rb 0- to 0+ decay from the momenta of the other products, using only the beta direction and not its energy. Several 0- to 0+ decays together produce about 30% of the higher-energy neutrinos from a reactor, and while in principle the theory is reasonably defined in terms of two nuclear structure-dependent matrix elements, there is inconsistency in the literature between difficult beta energy spectrum measurements in this type of decay. Simultaneous measurement of the beta-neutrino correlation will help us extract the two matrix elements to better test the 1st-forbidden theory. We expect to continue to maintain TRIUMF EEC high priority experiments for 2 graduate students at a time, so ask for additional funds to start a 3rd student while the 2nd student completes the analysis part of a Ph.D.

核衰变相关实验帮助建立了弱相互作用的本质，弱相互作用是一种自旋为1的玻色子（像光子一样，但质量很大）只与左轻子（即电子和中微子）耦合的理论。出射粒子的角度分布，如果测量到千分之一，对新的相互作用很敏感，这种相互作用可以产生具有不同手性的轻子。我们测量了在37K衰变中，相对于核自旋的β不对称性为β =-0.5706+-0.0018。这是C.S. Wu最初的违反宇称的观测结果，我们的β不对称测量在任何原子核或中子中都具有最佳的分数精度（即最小的不确定性/ β），并且与理论一致。我们的平均值可以约束产生错手中微子的相互作用，或者结合其他实验，测试具有有限自旋和磁矩的原子核是否都具有相同的衰变固有强度。我们将通过在37K中更好地测量Abeta和其他观测值来进一步探索这种可能的“守恒矢量电流”破坏。β对β能量的依赖仍在博士生的分析中，并且对新的4-费米子有效场论相互作用单独敏感。我们提出的测量，包括子核方向相对于初始核自旋的不对称性，探测产生错手正电子的新相互作用：这些可观察到的螺旋因子（电子质量）/（电子能量）的比例，通常在更高的能量下被抑制，使我们的测量互补。我们测量的关键是我们展示了用原子阱技术使原子核高度极化的能力，并通过原子原位方法确定原子核衰变的极化精度达到0.1%。我们还计划使用辐射β衰变产物的三个独立动量进行时间反转对称测试，这是第一代粒子在相对低能量尺度上的独特测试。反应堆中微子在总数和能量依赖性上表现出异常。我们正在从其他产物的动量重建92Rb 0-到0+衰变的中微子能谱，只使用β方向而不使用其能量。几个0-到0+的衰变一起产生了反应堆中约30%的高能中微子，虽然理论上该理论是根据两种核结构相关的矩阵元素合理定义的，但在这种类型的衰变中，难以测量的β能谱在文献中存在不一致。同时测量β -中微子的相关性将帮助我们提取两个矩阵元素，以更好地测试第一禁理论。我们希望继续同时为2名研究生维持TRIUMF EEC高优先级实验，因此要求额外的资金来启动第三名学生，同时第二名学生完成博士学位的分析部分。